Dental caries (tooth decay) remains a significant national and international health problem, especially in low- income and disadvantaged populations. Results of several clinical trials conducted outside the US (US studies have not been conducted) have suggested that glass ionomer cement (GIC) restorations used in a simplified and economic procedure known as atraumatic restorative treatment (ART) technique may be more successful than conventional dental treatments for large carious lesions with respect to increased restoration longevity and decreased caries recurrence. The reasons for the success of ART have not been clearly established, but it has been suggested that the GIC may interact with the caries affected tissue to restore a portion of its mineral content. Dental caries occurs when bacterial dental plaque combines with consumed, fermentable carbohydrates. This combination produces acids that penetrate and dissolves the tooth surfaces. GIC's are biocompatible materials having low technique sensitivity and release fluoride (F) which creates internal remineralization of a carious lesion. ART is an atraumatic technique as no drilling of teeth or anesthesia is required, thus making it advantageous in certain settings and situations. Amalgam is an alloy of mercury with another metal (silver) used traditionally by dentists to fill cavities in teeth. In Aim 1, we plan to conduct a prospective cohort study of initially 5 to 11 year-old children with at least one carious primary molar (1 to 3 surfaces cavitated) that has been restored with ART or amalgam. The children, patients at the Asian Health Services Dental Clinic in Oakland, CA and the CARECEN dental clinic in the primarily Hispanic Mission neighborhood of San Francisco, will receive initial dental assessments including pre-treatment radiographs, and treatment by staff dentists. Both clinics have agreed to participate and use both materials as part of their usual care. Patients that fit the child and tooth-level selection criteria will be recruited. Baseline clinical and radiographic evaluation of the ART and amalgam restorations, and 6-month and 12-month follow-up assessments (without radiographs) will be take place to assess clinical outcomes: a) caries recurrence, b) restoration retention, and c) restoration marginal integrity over time. In aims 2 and 3, analyses of the two restorative materials will be undertaken with restored teeth that naturally exfoliate during the study period. In Aim 2 we will examine the mechanical properties, microstructural characteristics of the restoration/tooth interfaces (Nanoindentation, and SEM-EDS) to identify changes induced in the tissues by the restorative materials and to provide insight to the mechanisms that could induce such changes. In Aim 3 we will evaluate the chemical changes of the restoration/tooth interfaces (RMS) to identify the presence of remineralization caused by the interaction of the dental materials (GIC and amalgam) with the dental tissues (enamel and dentin). A better understanding of the similarities and differences in the clinical, mechanical and chemical properties of these two materials when placed in primary teeth will help guide future recommendations for their use in the US. Public Health Relevance: This clinical translational observational study will allow us to evaluate the effectiveness of two dental restorative materials in two populations of high caries-risk children from lower socio-economic status households, many of whom rely on public assistance. One population is treated at the Asian Health Services Dental Clinic (AHSDC) in Oakland, California and the other at the Central American Resource Center (CARECEN) dental clinic in primarily Hispanic, Mission Neighborhood of San Francisco, California. This research will advance our understanding of the clinical outcomes of atraumatic restorative treatment (ART) vs. traditional amalgam techniques. ART has the advantage of being low cost, relatively easy to apply, especially to young children, and not requiring anesthesia and drilling of teeth. Additionally, the restored teeth will be collected after exfoliation to examine the remineralization process, and mechanical and chemical properties. If the results are favorable for ART with regard to restoration retention, marginal integrity, decreased caries recurrence, remineralization and other interactions with dental tissues, this type of treatment has the potential to impact dental practice, patient management policies, and public health.